[Wilds] Rename "--load-phutil-library" to "--library" in new arc

Summary: Ref T13098. The name of this option is needlessly obscure/verbose, and we now require it come first so it should be unambiguous even if we add arc borrow-a-book later.

Test Plan: Grepped for --load-phutil-library.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13098

Differential Revision: https://secure.phabricator.com/D19686